Model generation system having closed-loop extrusion nozzle positioning

Disclosed are methods and apparatus for fabricating a three-dimensional object in accordance with a computer-generated definition of the object that is stored within a memory. A method includes the steps of (a) evaluating the stored definition of the object to locate any un-supported features of the object; in response to locating an un-supported feature, (b) defining a support structure for the un-supported feature; (c) generating a fabrication tool movement list expressive of movements required by a fabrication tool to fabricate the object and any defined support structures; and (d) translating the fabrication tool in accordance with the generated fabrication tool movement list to fabricate the object and any defined support structures. The step of translating includes the steps of, generating a feedback signal that is indicative of at least one characteristic of a most recently fabricated portion of the object; and monitoring the feedback signal to detect a deviation of at least a location of the most recently fabricated portion of the object from a corresponding location as expressed in the associated portion of the fabrication tool movement list. Also disclosed are methods and apparatus for anti-aliasing aliased surface features of the object, representing the object definition in a vector format, generating a bit-mapped representation of the object, and an analysis of the definition of the object to identify and subsequently compensate for a region of the object that has a potential to retain heat during fabrication.